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• Today, 06:48 AM
Whoever gave you this problem clearly expects you to know that the area of triangle ABC is given by \frac{1}{2}\left|\vec{AB}\times \vec{AC}\right|. ...
1 replies | 20 view(s)
• Today, 06:36 AM
The equation of an ellipse with center at (x_0, y_0), semi-axis parallel to the x-axis of length a and semi-axis parallel to the y-axis of length b...
3 replies | 17 view(s)
• Yesterday, 12:32 PM
Is the problem to add the two numbers (not "the number) x+ y+ z and 3x+ 2y+ 3z? If so then you add "like terms"- terms that have the same...
3 replies | 42 view(s)
• Yesterday, 12:27 PM
An "arithmetic sequence" has some starting value, a and a common difference, d. The terms in the sequence are a, a+ d, a+ 2d, a+ 3d, …. In general,...
3 replies | 36 view(s)
• 09-17-2018, 08:23 PM
No, perhaps you are misreading. The problem said that the first car started "5 hours before the second", not 5 miles. Now, suppose that first...
5 replies | 118 view(s)
• 09-17-2018, 07:21 PM
Am I correct that "-3++ 11" means "-3+ (+11)", that "+125+- 40" means "125+ (-40)" and that "+5+- 7" means "+5+ (-7)"?
2 replies | 41 view(s)
• 09-17-2018, 07:17 PM
x hours (x> 5) the first car will have gone 18x miles. The second car, which will have been driving for x- 5 hours, will have gone 32(x- 5) miles. ...
5 replies | 118 view(s)
• 09-17-2018, 08:30 AM
You don't "have to" and, personally, I prefer to use the basic definition of "eigenvector". Since 1 is an eigenvalue, there must exist a vector...
3 replies | 89 view(s)
• 09-17-2018, 07:49 AM
Have you never taken an arithmetic class? The "decimal point" always means "add". Sometimes a raised dot is used to mean multiplication, as in...
21 replies | 440 view(s)
• 09-16-2018, 08:58 AM
Another way to do this is to note that \sum_{n=1}^\infty na_nx^{n-1} is the derivative of \sum_{n= 0}^\infty a^nx^n so letting f(x)= \sum_{n=...
2 replies | 133 view(s)
• 09-15-2018, 03:52 PM
You say you know how to do it "manually"- what is that method? I can see that 3^2= 9 so 3^4= (3^2)^2= 9^2= 81 while 3^3= 3(9)= 27 and then 3^7=...
6 replies | 113 view(s)
• 09-15-2018, 03:23 PM
All you have done is repeat the non-sense in your first post. You can't do arithmetic with "infinity" (unless you want to go to "non-standard"...
7 replies | 122 view(s)
• 09-15-2018, 07:40 AM
Well, in the problem here a= 1 and r= 2/9. What do you get when you put those in? (And please don't tell me you are using a calculator to do...
8 replies | 174 view(s)
• 09-13-2018, 07:28 AM
Seriously? If A and B are two numbers then if A- B is positive, A is greater than B. If A- B is negative then A is smaller than B.
21 replies | 440 view(s)
• 09-12-2018, 09:27 PM
More precisely, B= Yes, that is correct. Do you mean the eigenvectors of B? Yes, an eigenvector of B corresponding to eigenvalue 5 is...
2 replies | 164 view(s)
• 09-12-2018, 08:26 PM
Was there not a "part a" to a previous question? If your question is specifically about the phrase "part a shown" then perhaps you are parsing it...
9 replies | 226 view(s)
• 09-12-2018, 06:40 PM
Frankly, I have no idea what "known unknowns" or "unbuildable reality" could mean! I think this person is just being overly dramatic hoping it will...
1 replies | 75 view(s)
• 09-12-2018, 07:12 AM
That's not what lev888 said. He said that, of the numbers listed, "0.45 0.46 0.47 0.475 0.48 0.49", and that are larger than 0.75, so "0.48 0.49",...
29 replies | 727 view(s)
• 09-11-2018, 06:38 PM
You got a quadratic equation in what variable? The line (3- 2t, 5+ 8t, 7- 4t) had "direction vector" <-2, 8, -4>. The line (-2t, 5+ t, 7- t) has...
10 replies | 192 view(s)
• 09-10-2018, 11:57 AM
Because those are not closest to 0.475!
29 replies | 727 view(s)
• 09-10-2018, 11:47 AM
Good to start with but in 2009 Anna's age is A+ 3 so "Anna is half of Becky's age" is A+ 3= (B+ 3)/2 and "Mary is six years older than Anna" is M+3=...
2 replies | 102 view(s)
• 09-09-2018, 03:45 PM
Okay, how is the Fourier transform defined?
2 replies | 96 view(s)
• 09-09-2018, 03:43 PM
No, that has 3 times the length of <-6, 7, 6> Instead: 1) Find the length of <-6, 7, 6> 2) Divide <-6, 7, 6> by that length to get a vector in...
3 replies | 103 view(s)
• 09-08-2018, 12:53 PM
Actually the notation used in Linear Algebra can be quite different from the notation used in quantum mechanics- though they are both talking about...
5 replies | 333 view(s)
• 09-08-2018, 08:39 AM
The "guessing method", referred to here, is probably what I would call "the method of undetermined coefficients" (that sounds better than...
1 replies | 142 view(s)
• 09-08-2018, 08:15 AM
No, you should have A∙e - C∙e = -A∙B but it would probably be better to write it as C∙e - A∙e = A∙B.
8 replies | 206 view(s)
• 09-07-2018, 01:53 PM
Notice, by the way, that the two conditions, b- a= 6 and ab= 3127, are sufficient to determine a and b. The fact that "a and b are prime" is just...
5 replies | 255 view(s)
• 09-07-2018, 09:53 AM
The crucial point in your previous post was that, after squaring both sides of \sqrt{a^2+ b^2}= a+ b, to get x^2+ b^2= a^2+ 2ab+ b^2, the "a^2+ b^2"...
7 replies | 194 view(s)
• 09-07-2018, 07:41 AM
Assuming that t and x are given on the two axes of a Cartesian coordinate system then, yes, the graph of "x= t" is a straight line. More generally,...
6 replies | 243 view(s)
• 09-06-2018, 10:20 AM
Taking "x" and "y" as constants and "a" as the independent variable is pretty much the opposite of standard notation but, okay! So we have...
4 replies | 988 view(s)
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